An important consideration for 135mm focal length on APS-C is... what will you be using the lens for? It is a short tele focal length (200mm equivalent). I made the choice to go with 135mm STF instead, but you may (and most people do) find 135/1.8 CZ to be more useful.

That said, I've been considering going to A99 eventually and have evaluated pros and cons of getting 24-70/2.8 zoom versus getting 30mm/1.4 (or 24mm/2), 50mm/1.4 and 85mm/1.4 primes instead, and couple them with 70-200G with 2X TC (or 70-400G). I already have 135mm STF (a very special lens but only useful if you engage in manual photography and are willing to deal with the demands of the lens... no focus confirm but works superbly with Focus Peaking).

The prime advantage is clearly in size, weight, cost, speed and an edge in IQ. The disadvantage is lack of flexibility (must carry more lenses, which negates size, weight and cost advantages).

If you feel 135mm/1.8 is a lens you could use regularly (given the field of view on A77), it is a great lens to have.